(1) Field of the Invention
The present invention generally relates to a voice recording method for a mobile communication apparatus, and more particularly to a voice recording method by which voice signals received by a mobile communication apparatus and a voice signal corresponding to a voice of a user of the mobile communication apparatus can be efficiently recorded and clearly reproduced.
(2) Description of the Related Art
In recent years, portable telephones have been developed and various types of portable telephones are being used by general subscribers. The portable telephones are telephones generally used in mobile communication. For effective utilization of frequency bands, digital-type portable telephones in which voice signals are digitalized at a low bit rate and transmitted have been put to practical use. With the spread of the portable telephone, various convenient functions have been added to the portable telephone. One of the various convenient functions is; a function called xe2x80x9cVOICE MEMOxe2x80x9d by which downward voices are recorded during a call. Another one of the various convenient functions is a function by which a voice of an operator is recorded in a stand-by state
FIG. 1 shows a structure of a conventional digital-type portable telephone having a voice recording function.
Referring to FIG. 1, the digital-type portable telephone has an antenna 100, a sharing unit 101, a transmitter 102, a receiver 103, a TDMA processing circuit 104, a codec 105, a controller 106, a microphone 107, a loudspeaker 108 and a recording memory 109. The codec 105 is formed of a coder and a decoder. By the codec 105, voice input to the microphone 107 is converted into PCM data (64 kbps) and the PCM data is further converted into voice data having a lower bit rate. In addition, the codec 105 converts received voice data having a low bit rate into the PCM data and then converts the PCM data into an analog signal. The analog signal is supplied to the loudspeaker 108, so that voice is output from the loudspeaker 108.
There are various types of digital-type portable telephones, so that there are various types of codecs. In order to realize efficient communication, a coding method at a lower bit rate is being researched.
In a case of recording received voice, it is an easy matter to record analog voice signals output from the codec 105 or corresponding PCM data in the codec 105. In addition, in a case of recording a voice of an operator, it is an easy matter to record analog voice signals output from the microphone 107 or corresponding PCM data.
However, the conventional voice recording method for the mobile communication apparatus has the following disadvantages.
In the mobile communication system, in order to effectively employ frequencies, the same frequency is employed in different service areas (zones). This system is referred as a cellular system. In this system, different frequencies are employed in zones adjacent to each other. Thus, when a user of the portable telephone is moved from a zone to an adjacent zone, in the portable telephone, a channel switching process for switching the frequency is carried out to continue the call. The channel switching process requires a transition time during which a frequency is switched to another frequency.
Thus, in the conventional digital-type portable telephone as shown in FIG. 1, when the frequency is switched, an error occurs in the voice data in the frequency transition. As a result, recorded voice has noises.
In addition, when the coding rate in the codec 105 is lowered, many channels can be set in a transmission band. In this case, the frequencies can be effectively employed. Thus, if a codec having a lower coding rate is developed, a portable telephone having a codec which operates in two modes using different coding rates can be made. This type of codec is referred to as a dual-rate codec. In a case of the portable telephone having the dual-rate codec, when the user calling through the portable telephone in a mode using a lower coding rate is moved into a zone in which only a higher coding rate is acceptable, the mode using the lower coding rate has to be switched to the mode using the higher coding rate.
However, the conventional portable telephone shown in FIG. 1 has the codec 105 using a single coding rate. Thus, a voice recording apparatus used for the portable telephone having the dual-rate codec has not yet been developed. Thus, in the conventional portable telephone having the dual-rate codec, when the mode of the coding rate is switched, voice is recorded with noises.
Accordingly, a general object of the present invention is to provide a novel and useful voice recording method for a mobile communication apparatus.
A specific object of the present invention is to provide a voice recording method for a mobile communication apparatus by which voice can be efficiently recorded.
Another object of the present invention is to provide a voice recording method for a mobile communication apparatus by which voice can be recorded so as to be clearly reproduced even if a channel switching operation or a mode switching operation is carried out in the codec.
The above objects of the present invention are achieved by a voice recording method for a mobile communication apparatus having a codec which codes first voice data into second voice data and decodes the second voice data into the first voice data, a memory in which the second voice data should be recorded and a silent data generating unit which generates silent data, the method comprising the steps of: (a) successively recording the second voice data in the memory; and (b) recording the silent data in the memory as a substitute for the second voice data which is in a first state while the second voice data is being recorded in step (a), the first state being a state in which the second voice data may be noise data.
According to the present invention, the silent data is recorded in the memory as a substitute for the second voice in a case where the second voice may be noises. Thus, voice can be recorded so as to be clearly reproduced even if the voice may be noises in a case where a channel switching operation or a mode switching operation is carried out in the codec. Thus, the voice which has been recorded can be clearly reproduced without noises.
Another object of the present invention is to provide a mobile communication apparatus in which voice is recorded according to the above voice recording method.
The above object of the present invention is achieved by a mobile communication apparatus having a voice recording unit, wherein the voice recording unit comprises: a codec which codes first voice data into second voice data and decodes the second voice data into the first voice data; a memory in which the second voice data should be recorded; a silent data generating unit which generates silent data; and a control unit which causes the silent data to be recorded in the memory as a substitute for the second voice data which is in a first state, the first state being a state in which the second voice data may be noise data.
It is preferable that the second voice data is recorded in the memory in a first period in which the codec does not generated voice data to be transmitted and received. In this case, the second voice data can be efficiently recorded in the memory having a small capacity.